environments Article Spatiotemporal Evaluation of PM10 Concentrations within the Greater Athens Area, Greece. Trends, Variability and Analysis of a 19 Years Data Series Konstantinos P. Moustris 1 , Ermioni Petraki 2, Kleopatra Ntourou 1, Georgios Priniotakis 2 and Dimitrios Nikolopoulos 2,* 1 Lab of Air Pollution, Department of Mechanical Engineering, University of West Attica, Petrou Ralli & Thivon 250, Egaleo, GR-12244 Athens, Greece; [email protected] (K.P.M.); [email protected] (K.N.) 2 Sector of Environment, Department of Industrial Design and Production Engineering, University of West Attica, Petrou Ralli & Thivon 250, GR-12244 Egaleo, GR-12244 Athens, Greece; [email protected] (E.P.); [email protected] (G.P.) * Correspondence: [email protected]; Tel.: +30-210-5381888 Received: 12 July 2020; Accepted: 2 October 2020; Published: 6 October 2020 Abstract: This work investigates the spatiotemporal variation of suspended particles with aerodynamic diameter less than or equal to 10 µm (PM10) during a nineteen years period. Mean daily PM10 concentrations between 2001 and 2018, from five monitoring stations within the greater Athens area (GAA) are used. The aim is to investigate the impact of the economic crisis and the actions taken by the Greek state over the past decade on the distribution of PM10 within the GAA. Seasonality, intraweek, intraday and spatial variations of the PM10 concentrations as well as trends of data, are statistically studied. The work may assist the formation of PM10 forecasting models of hourly, daily, weekly, monthly and annual horizon. Innovations are alternative ways of statistical treatment and the extended period of data, which, importantly, includes major economic and social events for the GAA. Significant decreasing trend in PM10 series concentrations at all examined stations were found. This may be due to economic and social reasons but also due to measures taken by the state so as to be harmonised with the European Directives concerning the protection of public health and the atmospheric environment of the European Union (EU) members. Keywords: PM10 data series; statistical analysis; spatiotemporal evaluation; Athens; Greece 1. Introduction Over recent decades, many scientists all over the world have investigated the health impact due to PM10 Lee et al. (2020) [1] studied the adverse health effects of particulate matter (PM) in the mortality of patients diagnosed with asthma in Seoul, Korea. They have found that average PM10 exposures are associated with non-accidental mortality in patients with chronic obstructive pulmonary disease (COPD) and especially those diagnosed with asthma-chronic obstructive (ACO). In addition, the adverse effects of PM10 exposure are reported to be more severe in women and never-smokers. Hwang et al. (2020) [2] studied the impact of air pollution on breast cancer incidence and mortality in South Korea. According to their results, no significant association is found between air pollutant exposure and breast cancer mortality rate except the exposure that is due to PM10 pollutants. Zanobetti and Schwartz (2009) [3] applied a city- and season-specific Poisson regression in 112 U.S.A cities in order to examine the association of the mean PM2.5 and PM coarse exposure with daily deaths. They also combined the city-specific estimates using a total approach of random effects by season and region. According to their results, there is an increased risk of mortality for all causes associated with the exposure to PM2.5, the corresponding risks are higher than those previously observed for Environments 2020, 7, 85; doi:10.3390/environments7100085 www.mdpi.com/journal/environments Environments 2020, 7, 85 2 of 13 PM10 exposure and the coarse particles are also associated with more deaths. Pope et al. (1992) [4], studied the daily mortality in relation to the PM10 pollution in Utah Valley (U.S.A) between April 1985 and December 1989. It was found that a local steel mill was a major source of particulate air pollution in the area, in which concentrations of ozone, sulphur dioxide and nitrogen dioxide are generally low. The total respiratory and cardiovascular mortality were found to be related to the 5-day 3 moving average PM10 concentration. The 24-hour average concentrations ranged up to 365 µg/m , with 5-day moving average concentrations of up to 297 µg/m3 in the observation period [4,5]. Finally, epidemiological studies have traditionally played an important role in deriving guideline values for airborne suspended particulate matter [6]. Due to the major concern on the adverse health effects of PM10 exposure, many researchers have studied the variations of PM10 time series concentrations in cities all over the world. For Athens, the Capital of Greece, a large number of papers have been published, which depict that PM10 pollutants are among the most problematic ones for its inhabitants [6–12]. The recordings of PM10 concentrations started in 2001 in the GAA. The measurements are performed by the Department of Environmental Protection of the Hellenic Ministry of Environment and Energy with a sampling 1 frequency of 1 min− . The present study employs a sub-series of the whole data-set; specifically, the average daily concentrations between 2001 and 2018 from five different PM10 monitoring stations installed within the GAA. This sub-series is considered more suitable for a long-term analysis because it averages the intra-day variations and minimises, consequently, the overall bias to the estimations. The methodological approach is multi-level. Descriptive statistics are employed to outline the general behaviour of the series. Mean monthly PM10 concentrations are utilised for each one of the five monitoring stations to find the seasonality of PM10 time-series. Furthermore, the annual trend of PM10 concentrations is investigated in order to be related with some measures that have been taken by the state during the examined time period, as well as with the Greek economic crisis. Then, the correlation between the mean annual PM10 concentrations with the annual number of exceedances (days with mean daily concentration above the European threshold of 50 µg/m3) is studied. Finally, the intraday variation of PM10 concentrations at the five examined locations is extracted to investigate the sources influence on the formation of hourly concentrations. The different approaches are analysed and discussed. 2. Materials and Methods 2.1. Experimental Aspects The urban complex of Athens and Piraeus (the port of Athens city) is a large urban area in the Attica peninsula which includes Athens city, Piraeus city and their suburbs. It extends mainly to the Attica basin and within the administrative boundaries of five Regional Units of the Attica Region: Central Sector of Athens, Southern Sector of Athens, Northern Sector of Athens, Western Sector of Athens and Piraeus. In a similar meaning, the term greater Athens area (GAA) is often used. The GAA has a population of about 2.6 million inhabitants, which corresponds to 69% of the total population of the Attica Region (National Census 2011). The GAA basin is surrounded by high mountains. More specifically, at the west side of GAA the mountain Egaleo (468 m a.s.l.) is located. At the north north-west side of GAA there is Parnitha mountain (1,413 m a.s.l.), at the north north-east side the Penteli mountain (1,109 m a.s.l.) and at the east side Ymittos mountain (1,026 m a.s.l.). The only opening of the GAA is located at the south region, the seaside of Saronic Gulf which is a part of Aegean Sea. The climate of the GAA is temperate and is characterised as a typical Mediterranean climate. In general, and according to the Hellenic National Meteorological Service (HNMS) [13], sunny days are very common, even in winter covering about 65.0% of the days of the year. Rains occur mainly from October to April but overall, the annual rainfall is very low and does not exceed 400–450 mm. The minimum monthly temperature (mean of daily minimum by month) is about 7.0 ◦C (January and February) and the maximum monthly temperature (mean of daily maximum by month) is about 32.0 ◦C (July and August) [13]. Finally, the prevailing winds are southerly (winds that blow from Environments 2020, 7, 85 3 of 13 south to north) [13]. Taking into account the topography of the west, north and east high mountains (Figure1), a major air pollution problem occurs due to the bad air circulation and the dispersion of the air pollutants in GAA. The bulk of the industry (over 95%) is located in the west and southwestern extremities of the industrial areas of the GAA (Figure1). More specifically, the industrial area is outside the urban area (yellow line in Figure1) and is located on the west-southwest direction. The remaining 5% of the industry corresponds to a large number of small industries and handicrafts, which are scattered throughout the city. This creates particular difficulties, both in the research of air pollution problems and their control. As aforementioned, this work utilises the mean daily PM10 concentrations between 2001 and 2018 from five air pollution monitoring stations (Figure1) located in the GAA. These stations are a part of the air pollution monitoring network which operates under the Hellenic Ministry of Environment and Energy (HMEE). The measuring technology of PM10 pollutants is performed via the absorption of β-radiation [14]. The calibration of PM10 analysers is done through the absorption of β-radiation emitted by a standard sample of pre-determined concentration. Figure1 depicts the map of the GAA and the location of the five air pollution monitoring stations. Table1 shows the characteristics of the five examined air pollution monitoring stations. Figure 1. The map of the GAA and the location of the five air pollution monitoring stations. 2.2. Statistical Analysis Initially descriptive statistical analysis is applied to the mean daily PM10 concentrations calculated from the full data set recorded by all examined air pollution monitoring station.